Readiness of Faiss Library Version Bump

[heemin32]

K-NN added custom patch on faiss library to support multi-vector. 709b448

Recently faiss library made a change in the HNSW.cpp code which conflict with implementation in K-NN. https://github.com/facebookresearch/faiss/pull/3190/files#diff-5335385bb9a771bae868c8c908725eda0a9de22f7c0781dd27488f3ed3e50b60

Because of the conflict, we cannot bump the faiss version. We need to make a change so that there is no conflict with the latest code in faiss library.

[jmazanec15]

Closing in favor of #1508